1. Field of the Invention
The present invention relates generally to a shock absorbing type steering column apparatus, and more particularly to a technology of switching over a collapse load of a steering column when a collision happens.
2. Related Background Art
If an automobile collides with another automobile, a structure or the like, a driver might suffer from a secondary collision with a steering wheel by inertia. Automobiles produced over the recent years have widely adopted a shock absorbing type steering shaft and a shock absorbing type steering column apparatus in order to prevent the driver from being injured in such an accident. The shock absorbing type steering column apparatus has such a structure that when the driver suffers from the secondary collision, the steering column comes off together with the steering shaft and normally gets collapsed simultaneously with the steering shaft, thus absorbing a collision energy on that occasion. A known collision energy absorption system is a ball system in which, as disclosed in Japanese Patent Application Post-Exam Publication No. 46-35527, metal balls are interposed between the outer and inner columns, and plastic grooves are, when collapsed, formed in the inner peripheral surface of the outer column and in the outer peripheral surface of the inner column. Another known system is an drawing system in which the energy absorbing member such as a steel plate and so on is, as disclosed in Japanese Patent Application Laying-Open Publication No.7-329796, held by any one of the outer and inner columns, and the energy absorbing member is drawn by an drawing member such as a pin or the like held by the other column.
In the shock absorbing type steering column apparatus described above, the steering column, when a predetermined collapse load acts thereon, get collapsed. The following problem, however, arises in such apparatus. Normally, the collapse load is set based on a kinetic energy when a driver having a standard weight secondarily collides with the steering wheel at a predetermined velocity. If the driver is, for instance, a female or one of small stature, the kinetic energy thereof becomes, as a matter of course, small, and hence the steering column does not get collapsed even though this type of driver collides with the steering wheel at the same velocity. Then, the collision energy is not absolutely absorbed. As a result, the shock absorbing type steering column apparatus fails to perform its essential function, and the driver might receive a large impact on the breast and the head.
According to Great Britain Patent GB2340457A, there is proposed a system for addressing the problem described above, wherein a hydraulic cylinder type collision energy absorbing mechanism is provided, an electronic control unit calculates a target collapse load based on driving parameters outputted from a car speed sensor, a driver weight sensor and others, and a hydraulic fluid inflow resistance of the hydraulic cylinder is changed by adjusting an opening/closing quantity of an electrically-driven valve provided in a hydraulic circuit of the collision energy absorbing mechanism, thereby switching over the collapse load. In this system also, however, there is still a problem in terms of the timing when the electronic control unit calculates the target collapse load. For example, it is desirable that the target collapse load be calculated based on the driving parameters inputted from the respective sensors at the collision; however, this is impossible in the case of using the electrically-driven valve and an electromagnetic actuator. Specifically, the electrically-driven valve and an electromagnetic actuator require a comparatively long period of time for their operations finish once started. Hence, even when the drive current is inputted from the electronic control unit after the primary collision, it is unfeasible to switch over the collapse load in the extremely short period of time before the driver suffers from the secondary collision . Such being the case, as a matter of course, the electronic control unit previously switches over the collapse load before the collision. Because the respective driving parameters momentarily change corresponding to a driving condition, however,. a proper collapse load cannot be obtained.
It is a primary object of the present invention, which was devised under such circumstances, to provide a shock absorbing type steering column apparatus capable of switching over a collapse load of a steering column just when a collision happens and thereby absorbing an impact upon a secondary collision irrespective. of changes in kinetic energy of a driver.
To accomplish the above object, according to one aspect of the present invention, a shock absorbing type steering column apparatus including a collision energy absorbing mechanism for absorbing a secondary collision energy of an occupant upon a collision of a vehicle, comprises an energy absorption quantity adjusting device for changing an absorption quantity of the secondary collision energy absorbed by the collision energy absorbing mechanism, at least one of operation state detecting sensors for detecting a state of the occupant or of the vehicle, a collision detecting sensor for detecting the collision of the vehicle, and an electric control device for controlling a drive of the energy absorption quantity adjusting device on the basis of a result of the detection by the operation state detecting sensor at the point of time when the collision detecting sensor detects the collision of the vehicle.
According to the present invention, the electric control device calculates the kinetic energy based on a result of the detection by each of the operation state detecting devices immediately after the collision, then sets a target collapse load from mappings stored in a ROM or from an arithmetic formula, and outputs a drive current to an actuator of the energy absorption quantity adjusting device.
According to another aspect of the present invention, a shock absorbing type steering column apparatus including collision energy absorbing mechanism for absorbing a secondary collision energy of an occupant upon a collision of a vehicle, comprises an energy absorption quantity adjusting device for changing an absorption quantity of the secondary collision energy absorbed by the collision energy absorbing mechanism, wherein the energy absorption quantity adjusting device involves the use of a gas generated by a gas generating device as an operation source thereof.
According to the present invention, for instance, the electric control device outputs, when finishing the setting of the target collapse load, the electric current to an igniter of the electric ignition type gas generating device, and drives pins and a cylinder constituting the switching mechanism of the collapse load by dint of the gas generated by this gas generating device.